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Tablets & Capsules January 2017 43 over the temperature range used in this study. By converting the volumet- ric airflow to standard conditions, it is possible to substitute the mass flow rate of the air with the "standard volu- metric flow rate." Thus, a second set of process conditions can be expressed as shown in Equation 6. For this study, Equation 6 was used to determine the target solution flow rate for the target inlet process air tem- perature of 35°C and a bed tempera- ture of 22°C using the "benchmark" process conditions. See Equation 7. Therefore, the solution flow rate was set at 8 grams per minute, and the starting inlet air temperature at 35°C. The airflow was elevated to the level used in the benchmark trial to keep the solution delivery rate from falling below the lower delivery limit of the solution pump. Color uniformity was evaluated visu- ally and by using a Konica Minolta CM-5 spectrophotometer to establish delta E (∆E) values. Figure 2 shows the instrument and the methodology used to establish the values. (In the L, a, b color scale, ∆E is a positive number expressing a difference between two colors.) The ∆E values were calculated using a color difference calculator [7]. The human eye begins to perceive a color difference at ∆E values greater than 1.5. Shininess (gloss) was calculated from the LSCI and LSCE values used in determining the ∆E values [8]. (LSCI and LSCE are abbreviations of 1) lightness value for specular compo- nent included and 2) lightness value for specular component excluded). Results and discussion Tablets were coated successfully at all temperatures, and the photo (next page) shows a representative sample. The tablets were visually appealing, Figure 2 Establishing ∆E values L*, a*, and b* values for SCI (Specular Component Included) were used to calculate the ∆E CIE 2000 (1.1.1) values Figure 3 Effect of different settings ∆E values at 4 percent coating weight gain 3.0 2.5 2.0 1.5 1.0 0.5 0.0 Process air flow rate (volume) Solution spray rate (mass) 2 × (T In - T Bed ) 100 × (57 - 40) 100 × (35 - 22) 7.6 to 8.4 g/min 10 to 11 g/min 1 1 2 2 = × Process air flow rate (volume) 1 × (T In - T Bed ) 2 Solution spray rate (mass) 1 × 40-43ºC 37-38ºC 24-28ºC 20-25ºC 19-22ºC Benchmark used as reference 0.5 0.94 1.02 0.71 Figure 4 Shininess of tablets coated at different process temperatures 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 40-43ºC 37-38ºC 24-28ºC 20-25ºC 19-22ºC Tablet bed temperature Tablet bed temperature Benchmark used as reference 0.364 0.432 0.448 0.433 0.451 had good color uniformity, and there was no visible difference between the tablets coated under the different con- ditions. The ∆E values ranged from 0.5 to 1.0 (Figure 3). An additional comparison was made between tablets with a 3 percent coat- ing weight gain and those with a 4 per- cent gain. Visually, there was no differ- ence in appearance or color. The ∆E = (6) (7)

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